Answer:
The mass extinction that occurred 250 years ago and the mass extinction that occurred 65 million years ago may have been caused due to gradual processes or due to the catastrophic effect.
The mass extinction that occurred 250 million years ago was caused to the sudden climatic change and lead to extinction of almost 95% of the population present at that time.
The extinction of dinosaur took place 65 million years ago due to the meteorite that hit the earth.